1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for manufacturing the same, and more particularly to a liquid crystal display device and its manufacturing method capable of reducing line degradation due to a short circuit between a gate bus line and a counter electrode, thereby enhancing a process yield.
2. Description of the Related Art
Generally, a liquid crystal display device is composed of a lower substrate provided with a TFT and a pixel electrode, an upper substrate opposed to the lower substrate and having a color filter, and a liquid crystal layer interposed between the lower and the upper substrate. In addition, spacers are distributed in the liquid crystal layer for maintaining a fixed distance between the lower and the upper substrate.
FIG. 1 shows the lower substrate having a conventional FFS (Fringe Field Switching) mode structure in a plan view.
Referring to the figure, a gate bus line 2 and a data bus line 4 are arranged on the lower substrate 1 while crossing over each other so as to define an unit pixel, and a thin film transistor (TFT) is disposed adjacent to an intersection point of the gate bus line 2 and the data bus line 4.
A counter electrode 5 is a transparent conductor formed in each unit pixel. This counter electrode 5 includes a plurality of branches 5a disposed in an equal spacing, and a body portion 5b connected to one end of each branch 5a and joining its own counter electrode 5 to the counter electrode 5 of the adjacent pixel. In this case, a common signal is applied to the counter electrodes 5.
A pixel electrode 7 is formed in each unit pixel region in such a manner that it overlaps the counter electrode 5. The pixel electrode 7 includes a plurality of comb portions 7a, each extending parallel to the data bus line 4 and inserted between the branches 5a, and a bar 7b connected to one end of each comb portion 7a and contacting with a drain electrode of the thin film transistor (TFT). The pixel electrode 7 is also made of a transparent conductor. Further, the counter electrode 7 and the pixel electrode 7 are insulated from each other by interposing a gate insulating film therebetween.
On the other hand, an upper substrate (not shown) is opposed to the lower substrate 1 at a distance larger than that between the comb portion 7a of the pixel electrode 7 and the branch 5a of the counter electrode 5, which is not shown in FIG. 1. In addition, a liquid crystal layer having a plurality of liquid crystal molecules is disposed between the lower substrate 1 and the upper substrate.
The liquid crystal display device of the above-mentioned structure having a high aperture ratio and a high transmittance is operated as follows.
When a voltage is applied between the counter electrode 5 and the pixel electrode 7, a fringe field E including a vertical component is formed between both electrodes 5, 7 because the distance between both electrodes 5, 7 is larger than the distance between the lower and the upper electrode. This fringe field E has an effect on the whole upper area of the counter electrode 5 and the pixel electrode 7, so that all of the liquid crystal molecules in the upper area of the electrodes 5, 7 are operated. Therefore, the high aperture ratio and the high transmittance can be realized.
In the liquid crystal display device having the FFS mode structure which is one of high transmitting-wide visual field angle techniques, the counter electrode 5 is formed by ITO (indium tin oxide) and then the gate bus line 2 and the common bus line 6 are formed by a gate metal of an aluminum (Al) series suitable for a larger area in order to prevent corrosion caused by etching of the ITO during a manufacturing process of the lower substrate.
Nevertheless, the so constructed conventional liquid crystal display device has a drawback that since all of the counter electrodes 5 are connected to the common bus line 6 and constructed in the same layer as the gate bus line 2, a short circuit is apt to occur between the gate bus line 2 and the counter electrode 5 when a particle 10 happens to be generated as shown in FIG. 1B. Thus, even if any one portion is short circuited due to the particle 10, a xe2x80x98highxe2x80x99 voltage is always applied to the gate bus line 2 to cause a defect of the gate bus line 2. This leads to a problem that a process yield for the FFS mode structure is lower by 20% than that for a Twisted Nematic (TN) mode structure.
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a liquid crystal display device and its manufacturing method, which limit degradation to only one pixel while maintaining a existing process layer structure as it is even if a short circuit occurs between the gate bus line and the pixel electrode in the same layer due to the particle, thereby increasing the process yield.
To achieve the objective, there is provided a liquid crystal display device in accordance with one aspect of the present invention, the liquid crystal display device comprising a plurality of unit pixels, each unit pixel comprising:
a pixel electrode formed in the shape of a plate on a lower substrate by patterning of a first transparent electrode and protruding at its lower end so as to be contacted with one terminal of a thin film transistor;
a common bus line spaced at a predetermined distance from the pixel electrode;
a gate bus line formed on the opposite side of the common bus line with regard to the pixel electrode;
a counter electrode formed over the pixel electrode by using a slit-shaped second transparent electrode and provided with a first contact hole so as to be connected to the lower common bus line; and
a data bus line intersecting with the gate bus line between two pixel electrodes in the adjacent unit pixel and provided with a second contact hole so as to be connected to the lower pixel electrode.
In the liquid crystal display device according to present invention, a size of the first contact hole is preferably 10xc3x9730 xcexcm.
Also, it is preferred that a size of the second contact hole is 6xc3x9720 xcexcm.
In the liquid crystal display device according to the present invention, a thickness of the pixel electrode is preferably 400 xc3x85.
Preferably, a distance between the common bus line and the pixel electrode is 5 xcexcm.
In the liquid crystal display device according to the present invention, it is preferred that the data bus line is composed of a laminate of molybdenum (Mo)/aluminum (Al)/molybdenum (Mo).
Furthermore, to achieve the above-mentioned objective, there is provided a method for manufacturing a liquid crystal display device in accordance with another aspect of the present invention, the method comprising the steps of:
forming a pixel electrode on a lower substrate by patterning a first transparent electrode, the pixel having the shape of a plate and protruding at its lower end so as to be contacted with one terminal of a thin film transistor;
forming a common bus line spaced at a predetermined distance from the pixel electrode and then forming a gate bus line;
performing a vapor deposition of a gate insulating film on the gate bus line and then patterning the gate insulating film;
performing a vapor deposition of four layers on the gate bus line and then forming an etch stopper layer and an active layer by patterning;
forming a counter electrode over the pixel electrode by using a slit-shaped second transparent electrode and then providing the counter electrode with a contact hole for connecting the counter electrode with the common bus line;
forming a data bus line in such a manner that it intersects with the gate bus line, forming a source/drain electrode and then providing the source/drain electrode with a second contact hole for connecting the source/drain electrode to the lower pixel electrode; and
coating a protective film on the resultant product and then opening the productive film by patterning for the preparation of a leader-bonding operation.